In multiple myeloma, International Staging System (ISS) Stage III is defined by which combination?

• A β2-microglobulin >5.5 mg/L and albumin <3.5 g/dL
• B β2-microglobulin ≥3.5 mg/L and serum albumin <3.5 g/dL
• C β2-microglobulin >5.5 mg/L (regardless of albumin) ✓
• D LDH >ULN and β2-microglobulin >3.5 mg/L

Explanation

The International Staging System (ISS) for multiple myeloma: Stage I = β2-microglobulin <3.5 mg/L AND albumin ≥3.5 g/dL; Stage II = neither I nor III; Stage III = β2-microglobulin ≥5.5 mg/L (regardless of albumin). The Revised ISS (R-ISS) adds LDH and high-risk cytogenetics to Stage III. Albumin determines Stage I vs Stage II rather than Stage III directly. Understanding the ISS precisely is important for staging and prognosis questions.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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